Microstrip reciprocal latching ferrite phase shifter



United States Patent O 3,539,950 MICROSTRIP RECllPROCAL LATCHING FERRITE PHASE SHIFTER Elmer Freibergs, West Long Branch, N.J., assignor to the United States of America as represented by the Secretary of the Army Filed July 23, 1969, Ser. N0. 844,122 Int. Cl. H03h 7/30 U.S. Cl. 33331 10 Claims ABSTRACT OF THE DISCLOSURE A microstrip reciprocal latching ferrite phase shifting device operating in either the digital or analog mode having a microwave ferrite forming an integral portion of the microstrip line wherein a difference in phase shift occurring between longitudinally and transversely magnetized states of the microwave ferrite is accomplished by using two separate ferrite members of low coercive force and high remanence, each combining with the microwave ferrite to form a distinct closed magnetic flux path and each member carrying a separate energizing windings for establishing a magnetic field within said microwave ferrite, which magnetic flux in the microwave ferrite portion of one of the closed magnetic flux paths being in a direction normal to the direction of propagation of the microwave energy and parallel to the magnetic field associated with the propagated microwave energy and the magnetic flux in the microwave ferrite portion of the other closed magnetic flux path being perpendicular to the magnetic field in the microwave ferrite portion of said one closed magnetic flux path.

The invention described herein may be manufactured, used, and licensed by or for the Government for governmental purposes without the payment to me of any royalty thereon.

BACKGROUND OF THE INVENTION This invention belongs to the broad class of digital ferrite phase shifting devices in which, by switching between two ferrite magnetization states, that is, by controlling the direction of magnetization of the ferrite relative to the direction of polarization of the magnetic field component of the energy being propagated, the permeability of the ferrite is changed. Thus the velocity of energy propagation in the device changes and this is equalivalent to a change in the delay or phase shift of the signal being propagated. The ferrite magnetization switching results, therefore, in a differential phase shift. By using a ferrite which remains in a state of remanent magnetization after removal of the magnetizing energy, the phase shift is retained and the ferrite phase shifting device is said to be latched; the device of the invention also falls within this classification of latched ferrite phase shifting devices.

Ferrite phase shifters of the reciprocal type are known in which ferrimagnetic macrowave toroids are placed either in a waveguide or along the central conductor of a strip line in regions where the propagated wave energy is linearly polarized. Such toroidal ferrite elements are bulky and are not adaptable for integrated circuit use and, moreover, the control wires often are inefiicient magnetization means for obtaining orthogonal magnetization states, and, in cases using an array of control wires, the ferrite construction becomes complicated as well as bulky.

Ferrite phase shifters of the non-reciprocal type have been designed in which the phase of the microwave signal propagating along a device in one direction is shifted by a given amount, while the phase of a signal propagating in the opposite direction is shifted, if at all, by a much smaller amount. Such non-reciprocal devices rely upon establishing a circularly polarized radio frequency field. In one such non-reciprocal phase shifter using either a strip line or a microstrip line, the signal conducting element of the line is contoured in such a manner as to establish a radio frequency magnetic field which is circularly polarized; whether the direction of the circular polarization vector is clockwise or counterclockwise will depend upon the direction of propagation, assuming a given direction of ferrite magnetization is maintained. The actual change in magnetization of the ferrite is that of reversing its direction, once it has been determined which direction of propagation is to be accepted. Such devices are not suitable for reciprocal phase shifting. Furthermore, such devices use a control wire or thin electrode through which a current is passed in either one of two opposed directions to establish the magnetizing field. Such control wires, in addition to being relatively inefficient ferrite magnetizing means, are positioned in the region of effective microwave energy propagation, thereby contributing to transmission losses.

One type of reciprocal phase shifter uses a strip line with the ferrite toroid sandwiched between the center sig nal conductor and the ground plates of the strip line. The electromagnetic wave propagation inthis strip line generally is not identical to that in the microstrip line phase shifter of the invention. The prior strip line phase shifter is somewhat bulky and is not readily adapted for use with integrated circuit components and systems. In contrast, the phase shifter of the invention is less bulky and the configuration is such that it can be combined easily with other components on a common substrate to form part of an integrated microwave system. Furthermore, in order to achieve proper contact between the ferrite toroid and the remaining elements of the strip line in the prior phase shifter, pressure must be applied to the entire phase shifting structure which often damages the ferrite toroids and degrades performance. One of the magnetization states of such a strip line device is attained by passing current through the centrally disposed signal-carrying conductor of the strip line, while the winding used for the other magnetization state must pass between the ferrite toroid and the two opposed ground plates of the strip line. In contrast, in the device of the invention, both orthogonal magnetization states are achieved by ferrite members isolated from the radio frequency field associated with the signal propagating along the phase shifting device. The intimate contact that is required between applicant ferrite toroidal members and the corresponding surfaces of the microstrip line is readily attained with the device of the invention.

SUMMARY OF THE INVENTION In accordance with the invention, a microstrip reciprocal latching ferrite phase shifting device is provided which is readily adaptable for use with integrated and miniaturized microwave circuits. The phase shifting microwave ferrite is in the form of a thin slab 'Which can form part of the integrated circuit substrate. One side of this ferrite slab is completely metalized to form the microstrip ground plate and a narrow central portion of the opposite side of this ferrite slab is metalized to form a microstrip line signal conductor. The multiply-plated microwave ferrite slab, in addition to forming a microstrip line for propagating a desired mode of microwave energy, also can be part of an integrated circuit, allowing connections to be made readily to other integrated circuit elements.

In order to effect a differential phase shift of the microwave signal propagating along this microstrip line, the propagation constant of the line is changed by switching the microwave ferrite between a first magnetization state wherein it is magnetized parallel to the direction of microwave propagation and perpendicular to magnetic field associated with the propagated microwave signal and a second magnetization state wherein the ferrite is magnetized in a direction transverse to the microwave propagation and parallel to the magnetic field associated with the propagated microwave signal. Since both states of magnetization are reciprocal, the phase shifting device is reciprocal.

The transverse state of remanent magnetization of the microwave ferrite slab is achieved by passing a current pulse through a magnetizing coil wound lengthwise about a first ferrite member of more or less channel-shaped crosssection which, together with the microwave ferrite slab (substrate), forms a first closed toroidal magnetic flux path. The magnetic flux thus produced passes transversely to the microwave ferrite slab so that the latter is magnetized in a direction normal to the direction of propagation of the microwave signal and parallel to the direction of the magnetic field associated with the microwave signal. In this magnetization state, little or no interaction occurs between the magnetic field associated with the propagating microwave signal and the magnetic flux flowing within the ferrite. Consequently, the phase shift is minimal.

The longitudinal state of remanent magnetization of the microwave ferrite substrate is achieved by passing a short current pulse through a magnetizing coil wound transversely about a second ferrite member which is in the form of a plate and is disposed adjacent, and in contact with, the completely metalized side (ground plate) of the microstrip line. The planar ferrite member in conjunction with the microwave ferrite slab, forms a second closed toroidal magnetic flux path and the magnetic flux thus produced by the current in the transverse turns of the coil passes longitudinally along the microwave ferrite slab; that is, the latter is magnetized in a direction parallel to the direction of propagation of the microwave signal and normal to the direction of the magnetic field associated to the microwave signal. In this magnetization state the effective permeability of the ferrite is substantially changed and considerable phase shift now occurs.

The two ferrite members may be made of any ferrite having high remanence and low coercive force and, although they may be made of microwave type ferrites, this is unnecessary, since the two ferrite members are isolated from the microwave field and are used only to provide return paths for the magnetic flux passing through the microwave ferrite slab. These ferrite members preferably should have a higher coercive force than that of the microwave ferrite slab in order to achieve the highest possible remanent magnetization for latching purposes and for attaining the maximum possible phase shift per unit length.

The channel-shaped ferrite member can readily be isolated from the field along the microstrip cricuit by having contact with the microwave ferrite slab made only along longitudinal edges thereof distant from the center signal conductor near which the microwave field is concentrated. The planar ferrite member is isolated from the microwave field by means of the ground plate positioned between the microwave ferrite slab and the planar ferrite member.

The two ferrite members, in addition to serving as the return paths for the magnetic flux passing through the microwave ferrite slab, also provide effective shielding of the ferrite phase shifting microstrip circuit from external magnetic fields. Moreover, the planar ferrite member may, in some instances, be used to provide valuable additional support for the microstrip circuit, particularly in applications where greater ruggedization is essential or where the microwave ferrite slab is relatively thin. Furthermore, since these two ferrite members are isolated from the microwave magnetic field, they do not have to be made of a ferrite material suitable for microwaves; microwave ferrites are more expensive and the design criteria for such ferrites is more restrictive. As stated previously, it is necessary only that the two ferrite members be made of a ferrimagnetic material having good square loop characteristics, that is, high remanence and low coercive force, in order to provide the maximum possible remanent magnetization and minimum energy input supply, and thus achieved the maximum possible phase shift per unit length. The magnetizing means for the microwave ferrite, being positioned substantially coextensive with the microstrip ferrite circuit, is more eflicient than the control wires used in prior art devices.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view showing a ferrite phase shifter in accordance with the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing, FIG. 1 illustrates a microstrip ferrite phase shifting device 10 for shifting the phase of microwave signals and including a microstrip line 12 comprising an electrically conductive ground plate or plane 13 and a centrally disposed narrow signal conductor 14 spaced from the ground plate by a substrate 15 which will be described subsequently in greater detail. Such microstrip circuits, in which the electromagnetic wave is propagated through the dielectric medium bounded by the strip conductor on one side and the electrically conducting ground plane on the other side, are compact, wide-band devices and, since the dielectric medium of the microstrip line may also serve as a portion of the substrate of an integrated circuit upon or within which various circuit elements may be formed, such microstrip lines are very popular. Both the narrow signal conductor 14 and the ground plate 13 may be in the form of thin metallic platings, for example, a thin film of copper deposited by any one of several well known material deposition techniques. The ground plane is formed by completely metallizing one side of substrate 15. The radio frequency field associated with the microwave signal is concentrated in the substrate region between the center conductor strip 14 and the ground plate 13 and is absent in regions two or more strip widths above the signal-carrying conductor 14 and about three to four or more strip widths from the center of the microwave ferrite slab 15. The width of the signal-carrying conductor strip 14 and the thickness of the substrate 15 is determined by the application under consideration.

Since the operation of the device 10 depends upon interaction of the linearly polarized component of the magnetic field associated with the microwave signal propagating along the microstrip line 12, and the magnetic field in the microwave ferrite, the dielectric substrate 15 can be made of ferrimagnetic material suitable for operation over the range of microwave frequencies of the device. Such a material is characterized by high resistivity and by low loss over the microwave frequency range of interest. Henceforth, the substrate 15 will be referred to as a microwave ferrite slab 15.

As already mentioned, a difference in phase shift is produced as the direction of magnetization of the microwave ferrite slab 15 is changed from a direction transverse to the direction of propagation of the microwave signal, indicated by the light solid arrow to a direction parallel to the direction of microwave signal propagation, as indicated by the heavy solid arrow.

Means must now be provided, in addition to the integrated circuit microstrip line 12, to complete the flux path indicated by the heavy and light solid arrows. The means for completing the flux paths comprise a first ferrite member 21 and a second member 22. Members 21 and 22, as already pointed out, may be ferrites suitable for operation at relatively low frequencies and, low coercive force for low energy switching requirements and, for digital operation, should have high remanence, so that the state of magnetization of the microwave ferrite slab produced in response to short energizing pulses will remain after removal of said pulses.

The first ferrite member 21 used for producing transverse magnetization of the microwave ferrite slab 15 has a substantially channel-shaped cross-section and extends along the phase shifting device 10. The channel-shaped member 21 includes a pair of projecting leg portions 21a and 21b, the ends of which contact the microwave ferrite slab 15 along ar adjacent opposite longitudinal edges thereof. A first longitudinally disposed winding 25 is wrapped about the leg portions 21a and 21b of ferrite member 21. The winding 25, as indicated in FIG. 1, comprises two separate portions 25a and 25b wound about respective leg portions 21a and 21b of ferrite 21. The portions of winding 25 are wound in reverse direction relative to one another. It is possible, of course, to use but a single winding disposed about one only of the two leg portions. The magnetic flux created by the two portions 25a and 25b of winding 25 is shown by the light dashed arrows. The channel-shaped ferrite member 21 combines with the microwave ferrite slab 15 to form a closed magnetic loop or path, with the flux passing across said microwave ferrite slap 15 in the desired direction, indicated by the light solid arrow. The construction of the ferrite member 21 is such that the ferrite member does not interfere with the microwave energy concentrated largely in the central portion of the microstrip line 12 (the portion near the narrow signal conductor 14). Slight variations in the channel-shaped cross-section shown in FIG. 1 are permissible, of course; the essential requirements are (1) that the ferrite member 21 form a closed flux loop in combination with the microwave ferrite slab 15, (2) that the ferrite member 21 is exterior of the radio frequency field associated with the microstrip line effective in signal propagation, and (3) that the portion or portions of the ferrite member 21 about which the winding 25 is wound is large enough to accammodate said winding. The ends 27 and 28 of winding 25 connected to a pulse source 29 which may produce pulses of amperes or more and 5 to 10 microseconds, by way of example. The amplitude of the pulse and the pulse duration obviously are inversely related.

The second ferrite member 22 used for producing longitudinal magnetization of the microwave ferrite slab is a planar elongated element extending along the phase shifting device 10 and in proximity with the microwave ferrite slab 15. A winding 30 is wound about the planar member 22, as shown in FIG. 1, with the individual turns thereof being transversely disposed with respect to the length of the microwave ferrite slab 15. The terminals 32 and 33 of winding 30 are connected to either a pulse source 36, similar to the pulse source 29, or to an analog source 37, depending upon the position of switch 38. The magnetic flux passing through the microwave ferrite slab 15 during the longitudinal magnetization state arising from the flow of current through winding 30 is as shown by the heavy solid arrow. The planar ferrite member 22 combines with the microwave ferrite slab 15 to provide a closed magnetic loop distinct from that previously described. The return path for the longitudinal magnetic flux is along the planar ferrite member 22, as indicated by the dashed heavy arrow. The planar ferrite member 22 preferably includes several transverse slots 34 for receiving the transversely arranged turns of the winding 30, thus allowing the ferrite member 22 to be mounted in direct contact with the metallized surface 13 (the ground plate) of the microwave ferrite slab 15.

In practical operation, a pulse source 29 can be applied to the first winding 25. The flux set up in the closed path comprising the channel-shaped ferrite member 21 and the microwave ferrite slab 15 magnetizes the latter in the direction perpendicular to the direction of propagation of the microwave signal and parallel to the magnetic field associated with the microwave signal. This flux, which remains even after the pulse from source 29 has terminated, passing across the microwave ferrite slab 15 in the direction indicated in FIG. 1 by the light solid arrow, is in such a direction that no substantial interaction of the remanent flux with the magnetic field produced by the input signal arises owing to the magnetic properties of the microwave ferrite slab 15. There may be some phase owing to the dielectric nature of the microwave ferrite substrate 15; this effect will be present regardless of the magnetization state of the microwave ferrite slab 15. The transverse state of magnetization of the microwave ferrite slab 15 is the reference state.

If a pulse from pulse source 36 now is applied to the winding 30 surrounding the ferrite member 22, a flux is set up about the turns of winding 30 and the microwave ferrite slab 15 is magnetized in a direction parallel to the direction of micro-wave signal propagation and perpendicular to the magnetic field associated with the input signal, as indicated by the heavy solid arrow in FIG. 1. A phase shift now is introduced by virtue of the interaction of the magnetic field of the microwave signal with this longitudinally directed flux thus produced in the microwave ferrite slab. This phase shift is maintained, even after removal of the pulse from pulse source 36, because of the remanent flux in the closed path formed by the planar ferrite member 22 and the microwave ferrite slab 15.

Thus, by switching between pulses from source 29 and 36, a differential phase shift is provided by the phase shifting device 10; the actual difference in phase shifting between the two magnetization states will depend upon such factors as pulse magnitude and duration, number of turns on the windings 25 and 30 of respective ferrite members 21 and 22, the particular ferrimagnetic materials used for the ferrite members 21 and 22 and for the microwave ferrite slab .15, and the length of the microwave slab 15.

If, instead of switching between two distinct values of phase shift, as in the digital mode of phase shifting, one desires to operate in an analog mode, it is necessary only to energize the winding 30 on ferrite member 22 from a source 37 of continuous current which can be varied, depending upon the amount of phase shift desired. So long as a voltage of a given level from analog source 37 is applied to the terminals 32 and 33 of winding 30, a fixed amount of phase shift will be provided.

Although not shown in the drawing, certain modifica tions may be made in the device shown in FIG. 1. For example, where added strength is desirable, the entire assembly of FIG. 1 can be supported by a backing plate, such as a brass plate, in contact with the planar ferrite member 22. The slots in the bottom of the ferrite mem ber 22, as shown in FIG. 1, would allow for direct contact of the ferrite member 21 with such a backing plate. With such a construction, a coaxial input bracket could be mounted to the backing plate with the inner conductor thereof attached to the ends of the signal conductor 14 of the microstrip line 12. It should be understood that the ends of the center conductor of the microstrip line 12 of the phase shifting device 10 can be attached, as by short tabs, to various other circuit elements which may be formed on the common substrate 15.

What is claimed is:

1. A reciprocal latching phase shifter for shifting the phase of a linearly polarized microwave signal comprising a microstrip line for propagating said microwave signal along the length thereof including a ferrite slab having one major surface provided with a thin electrically conductive coating and the opposed major surface provided with a centrally disposed thin electrically conductive signal conductor; means for selectively switching the magnetization of said ferrite slab between two distinct magnetization conditions including a channel-shaped ferrite member having leg portions contacting said opposed major surface of said ferrite slab at regions remote fro-m said signal conductor, said channel-shaped member and said ferrite slab forming a first closed magnetic flux path, a planar ferrite member positioned adjacent said one mal jor surface and forming with said ferrite slab a second closed magnetic flux path, said members being constructed of ferrites of low coercive force and high remanence; a first coil wound longitudinally about at least one of said leg portions of said channel-shaped member, and a second coil Wound transversely about said planar member.

2. A reciprocal latching phase shifter according to claim 1 wherein said first coil creates in response to energization thereof a first magnetization state wherein the magnetic flux passes across said ferrite slab in a direction normal to the direction of propagation of said microwave signal and parallel to the magnetic field produced along said line by said microwave signal, and wherein said second coil creates in response to energization thereof a second magnetization state wherein the magnetic flux passes along the longitudinal edges of said ferrite slab in a direction parallel tothe direction of propagation of said microwave signal and normal to the magnetic field produced along said line by said microwavesignal.

3. A reciprocal latching phase shifter according to claim 2 wherein said planar member is in contact with said coating of the ferrite slab;

4. A reciprocal latching phase shifter according to claim 2 wherein said planar member contains transverse slots to provide spaces between said planar member and said coated ferrite slab for receiving the turns of said second coil.

5. In a reciprocal latching phase shifter for shifting the phase of a linearly polarized microwave signal propagating along a microstrip line in a given direction and having associated therewith a microwave magnetic field and wherein said microstrip line has a centrally disposed signal conductor and an electricallyconductive ground plate spaced from said signal conductor, comprising a ferrite slab for mounting said signal conductor and said ground plate on opposite major surfaces'thereof, a first ferrite member contacting the surface of said ferrite slab on which said signal conductor is disposed at regions displaced from saids ignal conductor and forming with said ferrite slab a first closed magnetic flux path, a second ferrite member positioned adjacent the surface of said ferrite slab on which said ground plate is disposed and forming with said ferrite slab' a second closed magnetic flux path, first magnetic field producing means carried by said first ferrite member for creating a magnetic flux traversing said ferrite slain in a direction normal to the direction of propagating of said microwave signal and parallel to the magnetic field associated with said signal and second magnetic field producing means carried by said second ferrite member for producing a magnetic flux passing along said ferrite slab in a direction parallel to the direction of propagation of said microwave signal and normal to the magnetic field associated with said signal.

6. A phase shifter according to claim 5 wherein said first ferrite member is a channel-shaped member having portions contacting said ferrite slab at regions isolated from said microwave field.

7. A phase shifter according to claim 6 wherein said first magnetic field producing means includes a coil having individual loops wound longitudinally about at least one of said portions of said first ferrite member.

8. A phase shifter according to claim 5 wherein said second magnetic field producing means is of planar configuration substantially coextensive With said ground plate and isolated by said ground plate from said microwave field.

9. A phase shifter according to claim 5 wherein said first magnetic field producing means includes a coil having individual loops wound transversely about said planar first ferrite member.

10. A phase shifter according to claim 5 wherein the portions of said first and second closed flux paths formed by said ferrite slab are orthogonal to one another.

References Cited UNITED STATES PATENTS 8/1968 Belson 333-41 11/1969 Simon etal 333 -31 US. Cl. X.R. 33.3-21.1, 84 

